Electronic combination lock



April 2l, 1970 A. E. JOEL, .JR

ELECTRONIC COMBTNATION LOCK 2 sheets-sneu 1 Filed April 17, 1967 x .im @Il SL m mwh,

/m/EA/on A. E. JOEL, JR.

April 21, 1970 A. E. JOEL, JR

ELECTRONIC COMBINATION LOCK 2 Sheets-Sheet 2 Filed April 17, 1967 .Nunavut Q kblkb United States Patent O U.S. Cl. 340-147 3 Claims ABSTRACT OF THE DISCLOSURE A detector circuit and flip-Hop circuit arangernent forming part of a combination lock is set only after a predetermined input code is applied. After this arrangement is set, a storage circuit stores a random input code. The lock is now locked and may be left. To reopen the lock, a storage circuit-coincidence circuit arrangement recognizes a reapplication o-f the random code and resets all of the circuitry.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to electronic combination locks.

Description of the prior art Combination locks provide several advantages over key-operated locks. With a combination lock, for eX- ample, an authorized person need not be concerned with a key Which may be forgotten or lost. Furthermore, access by an unauthorized person who has found or stolen a key is eliminated. Still further, combination locks are frequently more pick-proof than key-operated locks.

Notwithstanding the above advantages, combination locks have not received as widespread use as key-operated locks. One reason for this lack of use is that they are easily locked by unauthorized persons. Another reason is that it is often diicult or impossible to change an opening combination so as to foil persons no longer authorized to open a lock.

SUMMARY OF THE INVENTION An object of the present invention is to restrict the locking of an electronic combination lock to authorized persons and, furthermore, to permit such persons to determine the code necesaiy to reopen it,

This and other objects are achieved in accordance with the invention by an electronic combination lock which is locked, or set, by a predetermined code. After setting, but before leaving. the lock, a random code is applied to and stored in it. At this point, the lock cannot be reopened, or reset, until this random code is again applied. A person may therefore be authorized to reopen the lock without having to be given the ability to set it. Furthermore, his authorization to reopen the lock is readily removed merely by using a different random code at the ti-me the lock is set.

Embodirnents of the invention include a predetermined code detector whose output is effective to remove an enabling potential at an output terminal and, furthermore, to enable a rst storage circuit. After a random code has been stored in this circuit, the circuit is made nonresponsive to further inputs while a second storage circuit is enabled. When the random code is stored in the second storage circuit, an output is produced by a coincidence circuit. This output is effective to place the embodiment back in its initial state.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a block diagram of an electronic combination lock embodying the invention;

FIG. 2 is a table showing the steps followed in operating the lock of FIG. 1 and the results produced by these steps; and

FIG. 3 is a block diagram at a predetermined code detector that may be used in the lock of FIG. l.

DESCRIPTION OF THE DISCLOSED EMBODIMENT A plurality of pushbutton switch assemblies numbered 1 through 9 and zero are shown at the right-hand side of FIG. 1. Connected to these assemblies are a plurality of horizontal leads H1 through H4, vertical leads V1, V2 and V3 and diagonal leads D1 through D5. The diagonal leads are all connected to a direct current source 11 while the remaining` leads form a cable 12. The operation of any one of the pushbuttons causes a direct current voltage to appear on the vertical and horizontal leads associated with that button. The operation of button 5, for example, causes a direct current voltage to appear on leads H2 and V2.

Cable 12 is connected to a predetermined code detector 13. This detector has a reset input 14 and an output 15. When the pushbuttons are operated in accordance with a predetermined code, a voltage is produced at output 15. A detector that operates in this manner is disclosed in FIG. 3.

Cable 12 is also connected to storage circuits 16 and 17. These two circuits are identical and include pluralities of flip-flop that register, when enabled, the operations of the pushbuttons. Circuits 16 and 17 have enable inputs 18 and 19 and reset inputs 20 and 21, respectively.

(In the following discussion a Hip-iiop is assumed to have ONE and ZERO side outputs. In its reset, or initial, state, the ZERO side output is a binary ONE 'while the ONiE side output is a binary ZERO. In its set state, the binary ONE and ZERO outputs are reversed. This is sho-wn in the key in FIG. 2.)

The ZERO sides of the hip-flops in storage circuit 16 are applied to an AND gate 22 and a coincidence circuit 23. AND gate 22 produces a binary ONE output only when storage circuit 16 is in its reset state.

The ZERO sides of the flip-Hops in storage circuit 17 are similarly applied to coincidence circuit 23. Circuit 23 produces a binary ONE output when the outputs of circuits 16 and 17 match one another. Circuit 23 is conventional in nature and may take the form of a plurality of individual coincidence circuits feeding an AND gate.

The output 'of detector 13 is connected to the set input side of a flip-flop 24 by Way of a pair of normally open contacts L1 on la switch assembly L. When the predetermined code has been applied to detector 13 and contacts L1 are closed, ip-flop 24 is set.

The ZERO side output of flip-flop 24 is connected to an output terminal 25. The ONE and ZERO outputs appearing `on terminal 25 may be used as enabling and disabling voltages, respectively, to control any one of a number of devices. When used in a telephone handset, for example, the ZERO output would produce a disabling action so that the telephone could not be used by an unauthorized person.

As will become apparent from the following discussion, coincidence circuit 23 and AND gate 22 produce ONE outputs and iip-op 24 and detector 13 are in their reset states when the lock of FIG. l is in its initial or reset, state (i.e., when an enabling potential appears on terminal 2S). This is shown in the first step of the chart in FIG. 2. When the Ipredetermined code is applied by pushbuttons 1 through 9 and zero (causing a ONE output from detector 13) and contacts L1 are closed, flip-flop 24 is set and a disabling output is produced at terminal 25. At the same time contacts L1 are closed, a set of contacts L2 connected between the output of coincidence circuit 23 and reset input 14 are closed and detector 13 is reset. This is shown in the second and third steps of the chart in FIG. 2.

The ONE side of fiip-iiop 24 and the ZERO side of a flip-flop 26 are applied to an AND gate 27. Flip-flop 26 is initially in a reset state. The set input of fiip-fiop 26 is connected by way of a pair of normally open contacts L3 (which are part of switch assembly L) and an inverter 28 to the output of AND gate 22. Flip-Hop- 26 is not set, therefore, until the ZERO sides of storage circuit 16 produce other than all ONE outputs and contacts L3 are closed. This flip-flop is, therefore, still in its reset state when the third step of FIG. 2 has been executed. Consequently, AND gate 27 produces a ONE output at step (3) which enables storage circuit 16 so that it will register subsequent operations of pushbuttons 1 through 9 and zero.

The fourth step in the operation of the lock of FIG. y1 involves operating pushbuttons 1 through 9 and zero in a random but memorized code, or combination. The output of AND gate 22 is a ZERO so that the output of inverter 28 is a ONE. Switch assembly L is again operated which sets flip-flop 26 with the result that storage circuit 16 is disabled and storage circuit 17 is enabled. This is illustrated in step of FIG. 2.

In order to reinstate an enabling input at terminal (i.e., to reopen the lock), the pushbuttons must be operated in the previously stored random code. This may be done by the person originally setting the lock or by a person who has been authorized to unlock it. When the pushbuttons have been operated in accorddance with this code, the outputs of storage circuit 17 match the outputs of storage circuit 16 with the result that coincidence circuit 23 produces a ONE output as shown in step (6) of FIG. 2. The seventh and final step involves operating and releasing switch L. This step results in the performance of a number of functions. In particular, storage circuit 16 and detector 13 are directly reset, flipfiops 24 and 26 are reset in response to a ONE output from an AND gate 29 and storage circuit 17 is reset in response to a ONE output from an OR gate 30. When flip-flop 24 is reset, an enabling output is again produced on terminal 25.

From the above discussion, it is believed apparent that:

(l) Only a person knowing the predetermined code may set the lock,

(2) The lock may be reopened by anyone knowing the random code,

(3) A person may be authorized to reopen the lock while not being authorized to set it, and

(4) The reopening combination may be changed each time the lock is set, thereby readily preventing a previously authorized person from reopening the lock.

The lock will reopen in response to the random code only when storage circuit `17 is in its reset state upon application of the random code. It is possible, however, for this circuit to be in other than its reset state because once it has been enabled, it responds to any operation of the pushbuttons. In order to assure a reset state just [prior to applying the random code, a set of normally open contacts L4 are connected between the ONE side of flip-flop 26 and OR gate 30. Operation of switch assembly L just prior to use of the random code assures that storage circuit 17 is in its reset state.

One or rmore race conditions may exist when the 4 lock is constructed. Such conditions may be vovercome through the use of conventional techniques. As an eX- ample, Iwhen the lock is being reopened, one of storage circuits 16 and 17 may be reset before resetting has been completed elsewhere in the lock. Such a condition would remove the ONE output from coincidence circuit 23 and the remaining circuits would not be reset. This condition is readily overcome by placing a capacitor across the output of coincidence circuit 23 so that the voltage level cannot immediately change levels.

FIG. 3 shows a predetermined code detector that may `be used in the lock of FIGI. l. This detector is wired to particular vertical and horizontal leads of cable 12 so as to produce, when enabled, a ONE output when buttons 5 and 8 are operated in that order. In particular, when the detector is enabled and button 5 is operated, an AND gate 31 produces a ONE output which sets a fiip-fiop 32. When button 8 is then operated, an AND gate 33 produces a ONE output which sets a flip-fiop 34. The ONE output on the ONE sides of these two flip-flops are recognized by an AND gate 35 which, in turn, produces a ONE output on the detector output terminal 15.

The detector of FIG. 3 is reset Iwhen a ONE is applied to its reset input 14. In particular, such a ONE is applied directly to the reset side of fiip-fiop 34 and by Way of an OR gate 36 to the reset side of flip-flop 32.

This detector is also reset when an incorrect code is applied. That is, because leads V1, V3, H1 and H4 are connected to OR gate 36, the operation of pushbutton 1, 2, 3, 4, 6, 7, 9 or t? after the operation of pushbutton 5 causes fiip-iiop 32 to be reset.

It is believed readily apparent that the detector of FIG. 3 may be made responsive to other input codes by changing the 'wiring of the leads from cable 12.

I claim: 1. A combination comprising: first means which is set to product a particular output only after the application of a predetermined code,

second means connected to said first means to store,

only after said particular output is produced, a random code applied to said combination, third means connected to said second means to reset said first and second means upon the second application of said random code to said combination, and

output terminal means connected to said first means to make available said particular output.

2. In combination:

first means which produces an output in response to a predetermined code, second and third means each of which when enabled produces an output representative of a random code, fourth means producing an output in response to the simultaneous occurrence of said second and third means outputs,

means responsive to said first means output to enable said second means,

means responsive to said second means output to disable said second means and enable said third means, means responsive to said fourth means output to disable said third means, and

means responsive to said fourth means output to reset said first, second and third means.

3. In combination:

first means which produces an output in response to a predetermined code, second and third means each of which when enabled produces an output representative of a random code, fourth means producing an output in response to the simultaneous occurrence of said second and third means outputs,

a first fiip-fiop connected to receive a set input only after said first means output is produced, transmission means connected between said first flipflop and said second means to enable said second means when said first fiip-iiop is in its set state,

Ia second ip-op connected to receive a set input only after said random code has been applied to said second means,

means connected between said second Hip-flop and said transmission means to disable said transmission means when said second Hip-flop is in its set state,

means connected between said second Hip-flop and said third means to enable said third means when said second ip-op is in its set state.

means connected between said fourth means and said rst, second and third means and said first and second ilip-ops to reset each of said first, second and third References Cited UNITED STATES PATENTS 8/1960 McIlwain 340-171 XR 3/1967 Gerry 340--164 10 DONALD J. YUSKO, Primary Examiner U.S. C1. X.R. 

